1. Field of the Invention
The present invention relates generally to seals of the mechanical end face type and more particularly relates to contacting type end face seals for sealing mixers and other heavy duty uses.
2. Background Art
Mixers and agitators and other heavy duty uses of seals have been known to present a great amount of stress on the elements comprising the seals, especially the seal faces and seal rings. Wet running seals have been proposed which provide a buffer fluid between the seal faces of both an inboard and an outboard seal. Examples of such a seal are found in U.S. Pat. No. 4,721,311 issued to Kakabaker. Dry running seals, that is seals which have gas as a buffer fluid, are known, including those for pumping gas downstream from the high pressure side or the process fluid side toward the buffer chamber or a lower pressure side. An example of such a seal is found in U.S. Pat. No. 5,217,233, issued to Pecht et al, and commonly assigned to the assignee of the present invention.
Dry running gas seals are also known which have a dual seal arrangement in which the primary rings are rotating with the shaft and the stationary mating ring is sealingly connected to the housing. Dry running gas seals utilize gas as the sealed fluid.
For gas seals which do not have plural spiral grooves in the face of one of the seal rings, a fluid gap may be formed by introducing a pressurized gas between the seal faces during shaft rotation. However, because gas is compressible, differences in pressure are encountered across the radial profile of the seal face. The amount of pressure developed at a particular radial position necessarily depends on a number of factors. However, the compressibility of gases changes the forces which act to open a gap between the seal faces, and this change in forces may upset the delicate balance in the forces acting to keep the gap at a minimum distance to avoid fluid leakage while simultaneously avoiding high wear at the seal faces.